1. Field of the Invention
The present invention relates to a novel phosphine compound. More particularly, it relates to a novel phosphine compound which can be used as a useful catalyst in various asymmetric synthetic reactions by forming a complex with a transition metal such as rhodium, ruthenium, iridium, palladium and nickel. The invention further relates to a method for preparing chiral 3-hydroxybutanoic acid ester or chiral .beta.-butyrolactone derived from acetoacetic acid ester or diketene by asymmetic hydrogenation, respectively.
2. Description of the Related Art
Numerous transition metal complexes usable in organic synthetic reactions such as asymmetric hydrogenation reactions or asymmetric isomerization reactions are known. In particular, the complex coordinating an optically active tertiary phosphine compound in a transition metal such as rhodium, ruthenium or palladium is disclosed to have an excellent performance as a catalyst in asymmetric synthetic reactions in many reports.
Among tertiary phosphine compounds, in particular, 2,2'-(diphenyl phosphino)-1,1'-binaphthyl (hereinafter called BINAP) is one of the excellent ligands, and, using this BINAP as a ligand, a rhodium complex (Japanese Patent Application Laid-open (JP-A) No. 55-61937) and a ruthenium complex (Japanese Patent Application Laid-open (JP-A) No. 61-6390) have already been reported. Moreover, it has also been reported that 2,2'-bis(dicyclohexylphosphino)-6,6'-dimethyl-1,1'-biphenyl (hereinafter called BICHEP), and 2,2'-bis(diphenylphosphino)-6,6'-dimethyl-1,1'-biphenyl (hereinafter called BIPHEMP) are effective ligands as catalysts in, respectively, asymmetric hydrogenation reactions of .alpha.,.beta.-unsaturated carboxylic acids and carboxylic acid esters (Japanese Patent Application Laid-open (JP-A) No. 3-275691) and asymmetric isomerization reactions of allylamines (Japanese Patent Application Laid-open (JP-A) No. 63-135397).
However, numerous phosphine compounds developed for use as catalysts in such asymmetric synthetic reactions are not always sufficiently satisfactory in the aspects of selectivity, conversion ratio, optical purity, durability and the like depending on the intended reaction or reaction substrate to be used, and there has been a keen demand for development of a novel phosphine ligand for preparing a complex having a higher catalytic performance as compared with the conventional catalysts.